The one I like best is from Steve Lindsay. Very smooth and easy to move a vise on. I have an old GRS it works but not as smooth .
Others have used a Potters turntable and say they are good which makes sense, as it it built to hold wet clay.
I find on Aluminum, cutting the design first is the best. As stated by the best too many chances of a mistake. Bike parts have many raised areas and corners, a mistake can be disaster to fix.
Cut then clean out to add depth to your background area. The metal is thick enough to go deeper and...
Back when I did some of that I had the plating shop buff the stuff first. Supposedly none to be done after. Worked good, only one small issue I seen and the owner didn't. That item was one of a few left in the copper state while the others were chromed out.
If it is aluminum as a lot of MC parts it will probably go bad. If not right away it will in time. On brass some success Steel as well, but it is a crap shoot. It is a nerve wrenching thing if it starts to peel near the end of the job or shortly there after.
Remove all possible problems and...
One way my father did it many years ago when he had an engraving shop and had to engrave company logos or design. You enlarge the design then put it over a stiff card stock then go over it with a leather cutting swivel knife. He had done leather work for years and was pretty good at the process...